Carburetor Follies

[Guest]

I bought a GS850 about this time last year in a nearby town and rode it about 30 miles home. I noticed a flat spot at about 3,000 rpm on hard acceleration but otherwise O.K. I had it up to 70 mph for a short time without incident. The bike started with a brief push of the starter button and idled just fine at about 1,200 rpm.

When I got home I set out making sure the bike was roadworthy (fluids, etc). When I pulled the air box off I discovered there was no air filter within...ordered new OEM filter, also carb and airbox boots and o-rings and made sure airbox was sealed properly.

Tore into the carbs and got robertbarrs o-rings, soaked carbs in Berrymans and reassembled. The floats were grossly maladjusted so I reset to spec. I didn't pay too much attention to the various jets except to note that the main jets were the stock #115.

Threw the carbs back on started her up and it ran like s**t. Idle hung at 3,000 rpm for a few seconds then came down to about 1,500 but any touch of the throttle would kill the engine so I forgot about the carbs and got on to the wiring and other things.

Now that I'm back into the carbs I notice that the pilot jet is a #42.5 as opposed to the #40 specified in the docs on Cliff's Little Website. The pilot air jet is the #180 for the 45160 carb as opposed to the unspecified number for my 45110 carbs and what the f**k is the 1.7 mm main air jet and where can I find it? Likewise the starter jet...neither are mentioned in Mr. Nessism's tutorial (I don't think). The needle jet appears to be stamped 5-X 81E. Where is the number on the jet needle?

Anyway, I soaked the carbs again, rinsed them and blew them out with air and am ready to reassemble. I've got #40 pilot jets coming from Dennis Kirk and new pilot jet plugs along with new float needles.

The engine has good compression even at 38,000 miles.

Could this engine have been made to run at least marginally well just by dinking with the pilot jets and the float levels?

Thanks for any help you can offer. If you need more info just holler.

Rick

[Agemax]

as it ran so well before you stripped and cleaned the carbs, my guess is you have messed up somewhere in the rebuild or refitment. you should go back through everything and make sure it is all built and correctly fitted without anything missed out or adjusted wrongly

[Arley]

as it ran so well before you stripped and cleaned the carbs, my guess is you have messed up somewhere in the rebuild or refitment.

That's entirely possible, of course, but I'm pretty good at following written directions.
The major change here was going from a leaky airbox with no filter to a sealed airbox with filter. Some posts here suggest these bikes won't even run without the restriction of a filter. It's not *correctly fitted* with the wrong jets and float level.



Rick

[tom203]

As agemax suggests, retrace your steps. I'm suspicious of the "The floats were grossly maladjusted " stuff since it ran Ok before. Be sure that you measure the height correctly -it's easy to get confused

http://members.dslextreme.com/users/bikecliff/images/carbspec_float_height.html#A02

[Arley]

Let's approach it from a different direction

What effect is an oversize pilot jet and a leaky airbox with no filter likely to have on the performance of an otherwise stock GS850?

I may have done it wrong last time - I want to do it right this time.

Rick

[Arley]

What effect is an oversize pilot jet and a leaky airbox with no filter likely to have on the performance of an otherwise stock GS850?

I may have done it wrong last time - I want to do it right this time.

Rick

Anyone know?

[tom203]

Personally, I say the slightly oversized pilot jet and no filter might have caused the effect you described when you first rode bike

..."I noticed a flat spot at about 3,000 rpm on hard acceleration but otherwise O.K. "

but it doesn't explain your new problems after your carb work

[koolaid_kid]

An oversize pilot jet will make it richer on the idle circuit. It may have been installed to compensate for the leaky airbox with no filter, which would make it run leaner.
You don't care about the main air jet or starter jet.

[Arley]

Thanks guys.

When I discovered the air filter missing I was afraid of damage from a lean mix but compression was 140-150 on all cylinders so I'm hoping the valves didn't suffer.

I didn't measure float level until I reassembled the carbs the first time but they were all in excess of 24mm so I reset them to 22.4 or as close as I could get. Wouldn't the 24mm floats cause it to run even leaner?

[rustybronco]

Yes they would.

Have you looked at or changed the intake 'boot' o-rings yet? Are the intake boots in good shape and properly clamped?

[Arley]

Have you looked at or changed the intake 'boot' o-rings yet? Are the intake boots in good shape and properly clamped?

Carbs were rebuilt the first time as per instructions here and in nessism's tutorial.
New intake and airbox boots, ALL new o-rings from robertbarr.

Currently waiting for #40 pilot jets and hollow-ground screwdrivers which should be here tomorrow.

[Arley]

Well, got it running nicely.
Revs great and drops back to idle smoothly.
Got ready for a test ride and the starter puked. D*mn!

Try again this weekend.

Rick